The methods most widely used today for investigating alimentary functions and visualization of the alimentary canal comprise the use of radioopaque contrast media. However, the use of radioopaque media with X-rays to determine gastric emptying time or intestinal transit time, or to monitor the passage of material through the alimentary canal will subject the patient to high energy radiation in amounts which are often undesirable and furthermore offer only limited information on the functioning of the alimentary canal.
The radioopaque agent which is most often used for investigation of the gastrointestinal tract is barium sulphate, normally administered as a viscous suspension. Barium sulphate, however, has several disadvantages for this purpose. In particular, barium sulphate is known to change the movement of materials through the various parts of the intestines, which means that the results obtainec by using barium sulphate can hardly be taken as an indication of the functional state of the intestinal system, resulting in inadequate or even faulty diagnosis, which further results in inappropriate treatment.
It is also known to use soluble iodine compounds having a high radiodensity, typically tri-iodinated substituted benzene compounds, as X-ray contrast media for investigation of the alimentary canal. However, also with these agents, the patient will be subjected to undesirable amounts of high energy radiation.
Methods which do not rely upon the use of X-rays for the determination of gastrointestinal transit time have been used inert compounds such as carbon black and chromic oxide. In these methods, however, the transit time is determined by determining the interval between the time of an oral dose and the time of appearance of the compound in faces, and this means that no visualization of the alimentary canal and no differential diagnosis of the functional state of the various regions of the gastro-intestinal tract are obtained.
It is known from U.S. Pat. No. 4,115,540 and U.S. Pat. No. 4,243,652 that certain .gamma.-emitting radionuclides can be used in combination with certain carriers to provide multiple-units radiodiagnostic agents for investigation of the alimentary canal be scintigraphy which is normally performed noninvasively by means of a suitable instrument such as a .gamma.-camera or a rectilinear scanner, etc. It is also known to prepare single-unit tablets labelled with e.g. .sup.131 I or .sup.99m Tc for investigating the behaviour of pharmaceutical functions in the gastrointestinal tract.